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36 The test for strength based on the test method in ACI (2 lb/yd2) of binder and 5.4 kg/m2 (10 lb/yd2) of aggregate. 503R (13) should be used to determine whether the cleaning The second layer consists of approximately 2.2 kg/m2 (4 lb/ procedure, that is, size of shot, flow of shot, traveling speed yd2) of binder and 7.6 kg/m2 (14 lb/yd2) of aggregate. The of machine, and number of passes, is adequate to provide the resin content is approximately 25% by weight of the overlay. required minimum tensile bond strength. Figure 16 shows The thickness is about 6.4 mm (0.25 in.) the setup for the tensile bond strength on a test patch of the installed overlay. For tensile bond strength of 1.7 MPa (250 psi) or a failure at a depth of 6 mm (0.25 in.) or more into the concrete substrate, greater than 50% of the area is required. The result is based on the average of three tests on each test panel, which is normally at least 0.3 m by 0.9 m (1 ft by 3 ft). Because the test is temperature sensitive, the test cannot be performed above 27C (80F). One test result (three tests on one patch) is required for each span or 418 m 2 (500 ft2) of deck surface, whichever is greater. FIGURE 17 Applying epoxy to deck for multiple-layer overlay. FIGURE 16 Pull-off test to determine suitability of surface preparation or bond strength of overlay. INSTALLATION METHODS Primers Primers, if required by the manufacturer, should be compat- ible with the concrete repair materials and the first resin coat to be applied. Multiple-Layer Overlays Figures 17 and 18 show where binder (resin or monomer sys- tem) needs to be sprayed, squeegeed, or broomed on to the deck surface and followed by broadcasting gap-graded aggre- gate to excess over the surface. Figures 1921 show hand applications, chip spreader, and salting truck for applying aggregates. The aggregate must be allowed to spread out and fall downward into the resin, with the dust and fines carried FIGURE 18 Brooming epoxy over surface. off in the air. In hot weather, aggregate should be slowly and evenly built up on the surface until no wet spots are visible but Slurry Overlays before the resin begins to gel. After the binder has cured, the loose aggregate is removed from the deck and a second layer For MMA, a primer of monomer or resin system should be is applied. The first layer consists of approximately 1.0 kg/m2 applied at a rate of 0.41 0.14 kg/m2 (0.8 0.3 lb/yd2) fol-

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37 rate of 7.6 0.27 kg/m 2 (14.0 0.5 lb/yd 2). A binder seal coat of 0.68 0.14 kg/m 2 (1.3 0.3 lb/yd 2) is applied. The binder content is approximately 24% by weight of the over- lay (primer and seal coat). The thickness is about 7.6 mm (0.31 in) (6 ). Premixed Overlays Approximately 12% binder should be mixed with the aggregates. A primer is usually applied to the surface at a rate of 0.41 0.14 kg/m 2 (0.8 0.3 lb/yd 2) to improve the bond strength. The polymer concrete is placed and a vibra- tory screed is used to strike off and consolidate the PC. In some applications, continuous batching and paving equip- ment has been successfully used to place premixed PC. The FIGURE 19 Hand application of aggregates over resin. thickness is about 19 mm (0.75 in.) The polymer concrete could be consolidated to a relative compaction of not less than 97% in accordance with California Test Method 551. Wood screeds can be used to obtain good surface texture in the form of transverse irregular ridges for premixed PC (34). A suitable skid resistance can be achieved by placing grooves in the fresh PC or by broadcasting aggregates onto the fresh PC surface (15). Figure 22 shows the finished sur- face of an overlay. FIGURE 20 Chip spreader application of aggregates. FIGURE 22 Finished overlay surface. Material Handling, Mixing, and Placement Temperatures Handling and Mixing It is important that the handling and mixing of the resins and curing agents be performed in a safe manner that is accor- dance with the manufacturer's written recommendations. FIGURE 21 Salting truck for applying aggregates over epoxy. Illinois DOT requires that resins be stored in their original containers inside a heated warehouse in a dry area with tem- lowed by a slurry mixture of 2.7 0.27 kg/m2 (5 0.5 lb/ peratures maintained between 16C (60F) and 32C (90F) yd2) of binder and 6.5 0.54 kg/m2 (12 1.0 lb/yd 2) of man- Workers directly exposed to the resins are to wear protective ufactured-supplied filler. Gap-graded aggregate (as used in gloves and goggles. Material Safety Data Sheets should be multiple-layer overlays) is broadcast onto the surface at a prominently displayed at the storage site, as per the Illinois

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38 2007 TPO specification. Hsu et al. (47 ) provide a summary to 16C (60F) is the range of minimum temperatures for of safety requirements for using chemicals for concrete- epoxies reported by several DOTs. Some DOTs specify polymer materials. the same temperature for the deck and ambient; some use a slightly higher minimum temperature for the deck. Some Michigan DOT indicates that if the in-place material is DOTs specify the minimum temperature of the TPO com- defective, it is usually because of improper proportioning or ponents to be the same as the minimum ambient and/or deck mixing. Using different colors for multicomponent systems temperature. North Carolina DOT recommends that the helps to reduce proportioning errors (8). temperature be above 24C (75F). Missouri DOT has reported that an incorrect type of mix- Harper (7 ) suggests that for bridges with steep grades or ing paddle can lead to air bubbles in the epoxy, which results with super elevations, an upper limit on temperature be pro- in pitting on the surface of the TPO. Harper (7 ) recommends vided to prevent the resin system from becoming too low in that "jiffy" or "Sika" paddles be used. viscosity and ponding at the lowest elevation. Placement Temperatures The temperature of placement is important. Not all DOTs specify a minimum temperature for placement; 10C (50F)